In order for nuclear fusion to occur, the core of the sun must be hot enough to overcome the of the nuclei.

In order for nuclear fusion to occur, the core of the Sun must be hot enough to overcome the High Temperature and Densities of the nuclei.

It needs the conditions said as "High Temperature and Densities" for nuclear fusion to happen. In order for nuclear fusion, the core of the Sun must be hot enough to overcome the "high temperature" of the nuclei. The difference in mass between the reactants and products is shown as either the discharge or consumption of the energy when two or more atomic nuclei are joined to form one or more different atomic nuclei and subatomic particles. As we know that the Nuclei are positively charged so they move very fast which means the increase of temperature and the densities.